The field of this disclosure relates to imaging and collection devices and in particular to methods and devices for illumination, collection and imaging for optical code reading and other data and image capture devices.
Image capture and other data reading devices are used to read optical codes, acquire data, and capture a variety of images. One common data acquisition device is an optical code reader. Optical codes typically comprise a pattern of dark elements and light spaces. There are various types of optical codes, including 1-D codes (such as UPC and EAN/JAN barcodes) and 2-D codes (such as PDF-417 and Maxicode). For convenience, some embodiments are described herein with reference to capture of 1-D barcodes. However, the embodiments may also be useful for other optical codes and symbols as well as other images such as fingerprint capture, and nothing herein should be construed as limiting this disclosure to optical codes or particular types of codes.
One type of data reader is an imaging reader that employs an imaging device or sensor array, such as a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) device. Imaging readers can be configured to read both 1-D and 2-D optical codes, as well as other types of optical codes or symbols and images of other items. When an imaging reader is used to read an optical code, an image of the optical code or portion thereof is focused onto a detector array. Some imaging readers are capable of using ambient light illumination, while other imaging readers employ a light source to illuminate the item being scanned.
It is desirable for optical code scanners to have a wide dynamic range of usable illumination conditions over which they may operate. Typically, imaging optical code scanners are required to work in very low light conditions (such as in a dimly lit warehouse with ambient light intensity on the order of tens of lux) as well as in high light conditions (such as in full sunlight with light intensity over 100,000 lux). A lux is a unit of luminous incidence equal to one lumen per square meter. This large variation in ambient light conditions creates a required dynamic range of 10,000× or more. One possible method of compensating for the large variation of ambient light conditions is to equip the scanner with dynamic apertures or electronically adjustable attenuators. The present inventors have recognized that such compensation mechanisms add cost and complexity to the system and thus it would be desirable to provide a system that is entirely solid state, with no moving parts. The design challenge is to create a simple device with a broad dynamic range, which usually means electronically varying the integration time of the sensor as the primary means of exposure control.